1. Field of the Invention
The present invention relates to a zone controller for use in a zone controlled conveyor system. More specifically, it relates to one of zone controllers that enable construction of a conveyor line that is adapted for the shape or weight of the articles to be conveyed, by actuating adjacent zones for control solely or jointly by switching wiring and/or setting of the zone controllers.
2. Description of Related Art
A conventional roller conveyor system that has a conveying line divided into a plurality of control zones, each zone having a conveyor unit having a zone controller is disclosed, for example, in Japanese Laid-open Patent Application No. Hei. 11-199030.
The conventional roller conveyor system is equipped with a motorized roller and “free rollers” both for conveyance, the motorized roller and free rollers connected by belts spanned over them. Each unit has a photoelectric switch for detecting the presence of article and a “motor driver”, i.e., a controller, for controlling operation of the motorized roller.
Each of the zone controllers, connected to others, drives, brakes and stops the rotation of the roller depending on the signal of presence of article of its own zone and taking into account the signals of presence etc. transmitted from upstream and downstream zones. Such cooperative control by zone controllers achieves the “zero-pressure accumulating control” that enables conveying articles avoiding collision between articles.
More specifically, such roller conveyor system has a plurality of arranged units of a common shape, each unit corresponding to each control zone, the number of the units being that required depending on the length of the conveyor line, so as to enable the “zero-pressure accumulating conveyance” by means of distributed control.
Though such conveyor systems have advantage that they can meet many purposes by using units of a common shape and specifications, on the other hand, they have disadvantages that have been caused by the fact that the units have the same shape and the same conveying capability.
For example, as shown in FIG. 11, if the conveyed article W is longer than the unit U, normal “zero-pressure accumulation conveyance” cannot be made because the article W covers a plurality of units Ua and Ub. Therefore, when a long article is to be conveyed, it have to be positioned so that it extends crosswise to the length of the unit U, thus preventing stable conveyance.
As shown in FIG. 12, if the width of the conveyed article W is larger than the width of the unit U, the article W is supported unstably, thus preventing stable conveyance.
Moreover, even if the shape of the article W is within the limit of the unit U, in the case that the article W has a weight over the conveying capacity of the unit U or in the case that the unit Ub is positioned inclined upward or downward as shown in FIG. 13, disadvantage that driving force or braking force for the conveyance is not sufficient is caused.
Therefore, if stable conveyance adapted for various shapes and weights of the conveyed articles and inclining conditions of the conveyor lines is intended, a lot of conveyor units having various shapes and specifications should be provided, thus complicating construction of the conveyor line and increasing the cost. Improvement has been desired.
The invention disclosed in this application is proposed in consideration of the above-mentioned situations, aiming to provide a zone controller that enables conveyance of articles having various shapes and weights by means of actuating a plurality of units jointly by switching the modes of the zone controller of each unit and/or by changing wiring between the controllers.